1. Field of the Invention
Embodiments of the present invention are generally directed to a method and apparatus for stretch blow molding a container, such as a bottle. More particularly, embodiments of the present invention are directed to a tip for a stretch rod used during stretch blow molding that provides improved drop impact characteristics for the molded container.
2. Description of the Related Art
Stretch blow molding of containers generally comprises a first step of injection molding a preform made of a heat-softened amorphous polymer or other suitable material, and a second step of stretching and blowing the preform in a blow mold to form the final container. FIGS. 1-3 illustrate an exemplary blow mold 18 comprising a blow mold base 20 and left and right sides 44,46. As is known in the art, the blow mold 18 substantially mirrors an external shape of the container being molded. After the stretch blow molding is complete and the container is formed, the blow mold base 20 is vertically moved away from the formed container, and the left and right sides 44,46 of the mold 18 are horizontally moved away from the container.
Referring to FIGS. 1-3, the second step of stretch blow molding generally comprises inserting a stretch rod 14 into a neck 48 of the preform 16 (FIG. 1), generally centering the preform 16 on the stretch rod 14, stretching the preform 16 with the stretch rod 14, and injecting pressurized air into the preform 16 to force it to mold to the shape of the blow mold 18 (FIGS. 2-3).
The stretch rod 14 commonly includes a tip 22 at a general lower end 50 of a body 52 of the stretch rod 14. The tip 22 has a main body 24, and a lower end 28 of the body 24 is either flat or slightly rounded, as illustrated in FIG. 1. The tip 22 of the prior art stretch rod 14 is thus substantially blunt, which, as described below, introduces locations of potential failure to the molded container.
In more detail, the injection molded preform 16 commonly includes a sprue 38, illustrated in FIG. 1, which is formed at the lower end 34 of the preform 16 from an opening in the injection mold. In some stretch blow molding processes, such as injection stretch blow molding (“ISBM”), the sprue 38 is left intact prior to stretch blow molding. During the stretch blow molding process, the blunt tip 22 of the stretch rod 14 flattens or compresses the sprue 38 against the blow mold base 20, as illustrated in FIGS. 2-3. This method of accounting for the sprue 38 leaves a notch on an outside surface of the molded container that is aesthetically unpleasing, undesirably catches on clothing or other items, and presents a weakened area susceptible to fracture, cracking, shearing, or other failure during a drop impact.
In other stretch blow molding processes, such as reheat-blow (“RHB”), the sprue 38 is trimmed prior to blow molding. However, after the container is fully molded, remnants of the sprue form a rough notch on the outside surface of the container. As with ISBM, the notch presents a weakened area susceptible to fracture during a drop impact.
Accordingly, there is a need for an improved apparatus and method for stretch blow molding containers with reduced drop impact failure. More particularly, there is a need for an apparatus and method that does not severely compress and flatten the sprue so as to leave a notch on the outside of the molded container that is susceptible to drop impact failure. Further, there is a need for an apparatus and method of improving drop impact failure that can be implemented without significant additional cost or changes to the blow mold.